Question: Solve for $x$ and $y$ using substitution. ${-6x+3y = -3}$ ${y = x+3}$
Answer: Since $y$ has already been solved for, substitute $x+3$ for $y$ in the first equation. ${-6x + 3}{(x+3)}{= -3}$ Simplify and solve for $x$ $-6x+3x + 9 = -3$ $-3x+9 = -3$ $-3x+9{-9} = -3{-9}$ $-3x = -12$ $\dfrac{-3x}{{-3}} = \dfrac{-12}{{-3}}$ ${x = 4}$ Now that you know ${x = 4}$ , plug it back into $\thinspace {y = x+3}\thinspace$ to find $y$ ${y = }{(4)}{ + 3}$ $y = 7$ You can also plug ${x = 4}$ into $\thinspace {-6x+3y = -3}\thinspace$ and get the same answer for $y$ : ${-6}{(4)}{ + 3y = -3}$ ${y = 7}$